Silica-gel based antimicrobial composition having an antimicrobial coat of aluminosilicate on the surface of silica gel

ABSTRACT

The present invention provides a novel antimicrobial composition and a process for preparing the composition which composition is useful as antimicrobial and/or bactericidal material. The antimicrobial composition of the invention comprises silica gel and an antimicrobial coat of aluminosilicate on the surface of the silica gel, said composition having a pore volume of at least 0.3 cm 3  /g and a specific surface area of at least 100 m 2  /g. The aluminosilicate coat consists of either partial or complete substitution of ion-exchangeable metal ion (M) in aluminosilicate solid particles represented by the formula 
     
         xM.sub.2/n O.Al.sub.2 O.sub.3.ySiO.sub.2.zH.sub.2 O, 
    
     wherein x and y represent the numbers of molecules of the metal oxide and silicon dioxide, respectively, M is an ion-exchangeable metal, n is the atomic valence of M, and z is the number of molecules of water. One or more microbicidal metal ions selected from the group consisting of silver, copper, zinc, mercury, tin, lead, bismuth, cadmium and chromium are either partial or completely substituted for the ion-exchangeable metal ion (M).

RELATED APPLICATION

The present application is closely related to copending application,Ser. No. 751,969 filed Aug. 29, 1991 pending entitled "AntimicrobialCompositions Having Resistance To Heat And Weathers"

BACKGROUND OF THE INVENTION

The present invention relates to a novel antimicrobial compound and aprocess for producing it. Furthermore, the present invention relates toa novel antimicrobial polymer composite comprising a polymer and theantimicrobial composition.

Inorganic aluminosilicates in which their alkali metal salt component issubstituted by microbicidal metals have been known as antimicrobialcompositions but antimicrobial compositions of the type contemplated bythe present invention that are based on silica gel have not been known.In the conventional antimicrobial compositions based onaluminosilicates, microbicidal metals are uniformly distributed in theirwhole part including the surface and interior. In view of the structureof those compositions, not a large proportion of the microbicidal metalsused is considered to work effectively in actual applications. Suchbeing the case, the microbicidal metals have had to be used in largequantities in order to insure stronger antimicrobial activities.However, if antimicrobial compositions having high contents ofmicrobicidal metals are added to polymers, they are discolored orstained.

It is also known to have a silver compound retained on a silica matrixthrough physical adsorption by treating the silica with a solution ofsilver nitrate. A problem with this method is that silver, being notchemically bound to the matrix, is labile and will be readily separatedor released from the matrix.

The conventional aluminosilicate based antimicrobial compositions arecommercially available in powder form comprising fine particles of 1-20μm in size. In order to make them convenient for use in aqueous systems,the compositions must be formed into beads, pellets and other shapesthat have increased mechanical strength and water resistance. In shapingthe powder of conventional aluminosilicate based antimicrobialcompositions, a special wet forming method is practiced using bindersand other additives and the shaped part is then sintered at elevatedtemperatures to increase its strength. However, the thus shaped part ofantimicrobial aluminosilicates (amorphous) or antimicrobial zeolites(crystalline) are not suitable for prolonged use in aqueous systemsbecause if they are submerged in water, their water resistancedeteriorates gradually and in an extreme case they are disintegrated tofines which are no longer effective for the intended purpose.

SUMMARY OF THE INVENTION

The present invention has been accomplished under these circumstancesand has as an object providing a novel antimicrobial composition that isstable, that uses a smaller amount of microbicidal metals and that yetexhibits strong antimicrobial action.

Another object of the present invention is to provide a process forproducing this novel antimicrobial composition.

A further object of the present invention is to provide an antimicrobialpolymer composition using the novel antimicrobial composition.

The present inventors conducted intensive studies in order to solve theaforementioned problems of the prior art and found that they could besolved by providing the porous surface of silica gel with anantimicrobial coat of an aluminosilicate containing metal ions havingmicrobicidal action. The present invention has been accomplished on thebasis of this finding. The present inventors also found that an improvedantimicrobial polymer composition could be obtained by dispersing saidantimicrobial composition in a polymer.

DETAILED DESCRIPTION OF THE INVENTION

As is well known, silica gel is an amorphous porous material that ischiefly composed of SiO₂, represented by the general formula (SiO₂)_(x)(H₂ O)_(y), where x and y represent the numbers of molecules of SiO₂ andH₂ O, respectively. Silica gel has long been used extensively asdesiccants, adsorbents, catalyst carriers, and fillers in paper, rubber,plastics, etc. While silica gel is commercially available in granules,spherical beads or crushed products of various sizes, most of them havea SiO₂ content of at least 99.5%, with Na₂ O, Fe₂ O₃, MgO, CaO, Al₂ O₃,etc. being present as impurities in very small amounts. The physicalproperties of commercially available silica gel vary with manufacturer,but most of the products currently sold in Japan have pHs in the rangeof 4-8, a true specific gravity of 2.2, pore volumes of 0.3-0.8 cm³ /g,specific surface areas of 100-800 m² /g (as measured by the BET method;unless otherwise noted, the values of specific surface area that appearhereinafter are those measured by the BET method), and pore sizes of20-200 Å. Major sellers and manufacturers of silica gel in Japan areFuji Davison Co., Ltd., Asahi Glass Co., Ltd., Mizusawa IndustrialChemicals, Ltd. and Toyota Chemical Industries, Ltd. A major overseasmanufacturer of silica gel is Grace Chemicals, Co., which is producingsilica gel beads of different sizes (10-30 μm; 0.5- 1 mm; 1-3 mm) andphysical data (pH in suspension =5-7). Silica gel products presentlyavailable from Grace Chemicals, Co. have pore volumes of 0.3-1.8 cm³ /g,specific surface areas of 20-750 m² /g, and pore sizes of threedifferent ranges, large, medium and small. Wide porous silica gels ofXWP Series from Grace Chemicals, Co. have very large pore sizes rangingfrom 250 to 1,500 Å.

The silica gel to be used as the starting material in the presentinvention may be in the form of a powder, granules, beads or any othershaped parts. However, considering the case of performing a chemicaltreatment on silica gel by the method to be described below (i.e.,treatment with an alkali solution and an aluminate solution), silica gelin a fine form is preferred. A more preferred type is porous silica gelin which a great number of capillary pores are present to provide largepore sizes and specific surface areas. For example, silica gel that ispreferably used as the starting material in the present invention has apore volume of at least 0.3 cm³ /g, and one having a void volume of atleast 0.4 cm³ /g is more preferred. The pore size of silica gel ispreferably as large as possible, for example, at least 50 Å, morepreferably at least 70 Å. The specific surface area of silica gel is atleast 100 m² /g, more preferably at least 200 m² /g.

The silica gel material having these characteristics is preferred forthe following reasons. First, silica gel having the physical data listedabove is very porous and the capillary pores in it have a very activesurface. If such silica gel is chemically treated by the method to bedescribed hereinafter, whereby an aluminosilicate coat is formed on theactive surfaces of capillary pores, and if microbicidal metals areretained on that coat in a stable way by ion exchange, chemical speciesand metal ions that take part in reaction will diffuse rapidly enough topermit the intended chemical reaction to proceed smoothly on thesurfaces of pores in the silica gel. Further, as already mentioned, themicrobicidal metal in the antimicrobial composition of the presentinvention is distributed substantially uniformly on the surfaces ofpores in silica gel in a preferred way, so microbicidal metal ionsformed as a result of dissociation will diffuse rapidly through pores toinsure that those microbicidal metal ions contact bacteria or fungi overa sufficiently large area to inhibit their growth or kill themeffectively.

Microbicidal metal ions may be any metal ions that effectively exhibitan antimicrobial and/or microbicidal action and such microbicidal metalions are not limited to any particular kinds. Typical examples ofmicrobicidal metal are silver, copper, zinc, mercury, tin, lead,bismuth, cadmium and chromium, and these metals may be used either ontheir own or as admixtures.

The aluminosilicate coat formed on the surface of the silica gel matrixin the present invention is generally represented by the followinggeneral formula: ##EQU1## where x and y represent the numbers ofmolecules of the metal oxide and silicon dioxide, respectively; M is anion-exchangeable metal; n is the atomic valence of M; and z is thenumber of molecules of water. M is usually a monovalent metal such asLi, Na or K and may sometimes be NH₄ ⁺. If desired, such monovalentmetals or NH₄ ⁺ may be substituted either partially or totally with adivalent metal such as Mg, Ca, Sr, Ba, Mn, Ni, Co or Fe.

The coat made of the aluminosilicate may be either crystalline (zeolite)or amorphous or both (a combination of crystalline and amorphousphases). The thickness and composition of the aluminosilicate coat canbe properly adjusted by controlling various factors such as the physicalproperties of silica gel used as the starting material, the amount of ituse, alkali concentration, the amount of addition of a aluminate,reaction temperature and time. Irrespective of whether thealuminosilicate is crystalline or amorphous, the molar ratio of SiO₂ toAl₂ O₃ is preferably within the range of 1.4-40. Typical examples of thealuminosilicate that can be used in the present invention includezeolite A having a SiO₂ to Al₂ O₃ molar ratio of 1.4-2.4, zeolite Xhaving a SiO₂ to Al₂ O₃ molar ratio of 2-3, zeolite Y having a SiO₂ toAl₂ O₃ ratio of 3-6, an amorphous aluminosilicate or a mixture ofcrystalline and amorphous aluminosilicate that have SiO₂ /Al₂ O₃ molarratios of 1.4- 30.

The process for producing the antimicrobial composition of the presentinvention is described below. Briefly stated, the antimicrobialcomposition of the present invention can be obtained by first chemicallytreating porous silica gel with an alkali solution and an aluminatesolution and then forming an antimicrobial coat on the so treatedsurface of the silica gel.

The alkali solution may be a solution of an alkali metal hydroxide suchas NaOH, KOH or LiOH, with the aqueous phase being held in an alkalinecondition, for example, in a pH range of 9.5-12.5 during treatment. Anexample of the aluminate solution is a solution of an alkali metalaluminate such as NaAlO₂, KAlO₂, or LiAlO₂. The chemical treatment ofsilica gel with the alkali solution and the aluminate solution isperformed at either ambient or elevated temperatures. As a result ofthis chemical treatment, SiO₂ present on the surfaces of capillary poresin silica gel undergoes reaction to have an aluminosilicate coatcontaining an ion-exchangeable metal formed on the active surfaces ofpores. Subsequently, the coat is subjected to an antimicrobial treatmentto prepare the antimicrobial composition of the present invention. Foraccelerating the microbicidal speed to insure excellent antimicrobialand/or microbicidal activity, the antibacterial composition of thepresent invention should have a pore volume of at least 0.3 cm³ /g and aspecific surface area of at least 100 m² /g.

After the chemical treatment, silica gel is washed with water to removethe excess alkali and metal component present in the solid phase.Washing with water may be performed by either a batch method or a columnmethod. In the next step, silica gel is subjected to an ion-exchangetreatment for allowing antimicrobial and/or microbicidal metal ions tobe retained on the aluminosilicate coat so that it becomes antimicrobialand/or microbicidal. To this end, silica gel is treated with a neutralor weakly acidic solution of salts containing one or more microbicidalmetal ions selected from the group consisting of silver, copper, zinc,mercury, tin, lead, bismuth, cadmium and chromium. Useful examples ofsalts to be contained in the solution include: nitrates such as AgNO₃,Cu(NO₃)₂, AgNO₃ and Zn(NO₃)₂ ; sulfates such as ZnSO₄, SnSO₄ and CuSO₄-SnSO₄ ; perchlorates such as AgClO₄, Cu(ClO₄)₂, Zn(ClO₄)₂ and Cd(ClO₄)₂; chlorides such as ZnCl₂ and ZnCl₂ -CdCl₂ ; and organic acid salts suchas Ag-acetate, Zn-acetate, Cu-tartrate and Cd-citrate. One or more ofthese microbicidal metals are subjected to ion exchange at ambient orelevated temperatures with the ion-exchangeable metal (M) in thealuminosilicate coat, whereby a predetermined amount of the microbicidalmetal or metals are supported stably in the coat by ionic bonding toprovide it with a desired antimicrobial activity. In this way, thesilica gel based antimicrobial composition of the present invention isprepared.

The solution containing one or more microbicidal salts to be used in theion-exchange treatment may also contain metal ions having noantimicrobial activity. The degree by which the ion-exchangeable metal Min the aluminosilicate coat is substituted with microbicidal metal canbe adjusted by controlling the concentration or composition of the saltsolution containing the microbicidal metal, as well as the reactiontemperature or time for ion exchange. By controlling the conditions forpreparing the aluminosilicate coat and the conditions for ion exchangewith the bactericidal metal ion, the total amount of microbicidal metalscan be maintained at constant levels, say within the range of 0.003-0.5mmol/100 m² (of the surface area of an anhydrous antimicrobialcomposition). Adjusting the characteristics of the microbicidal saltcontaining solution in the manner described above, the followingadvantage is obtained. That is, when microbicidal metal ions such assilver, copper and zinc in the antimicrobial and/or microbicidalaluminosilicate coat formed on the active surfaces of capillary pores insilica gel undergo hydrolysis, products such as oxides and basic saltsare formed to contaminate the antimicrobial coat, whereby the inherentantimicrobial and/or microbicidal activity of the composition willdeteriorate. However, this problem can be avoided by proper adjustmentof the microbicidal salt containing solution. In place of performing ionexchange using the microbicidal metal ion containing solution, organicsolvents such as alcohols and esters, or mixtures of solvents and watermay be used to perform the intended ion exchange. For instance, if analcoholic solvent such as methyl alcohol or ethyl alcohol is used insubstituting the ion-exchangeable metal M in the aluminosilicate coatwith Sn²⁺ which is a highly hydrolyzable microbicidal metal ion,precipitation of SnO, SnO₂, basic tin compounds, etc. on the coat can beprevented to insure that the antimicrobial activity of the coat will notdeteriorate.

After the treatments described above, silica gel is washed with wateruntil no microbicidal metal ions are detected in the filtrate.Thereafter, silica gel is dried at 100°-110° C. to complete the processof preparing the antimicrobial composition of the present invention. Ifa specific use of the compound needs further reduction in the watercontent, it may be dried under vacuum or dehydration may be performedwith the heating temperature elevated to 200°-350° C.

To achieve excellent antimicrobial and/or microbicidal activity againstbacteria and fungi or to insure anti-algal effect, the total content ofmicrobicidal metals in the antimicrobial composition of the presentinvention is preferably at least 0.003 mmol/100 m² (of the surface areaof the composition in anhydrous state), more preferably at least 0.005mmol/100 m². Usually, the range of 0.03-0.5 mmol/100 m² will suffice. Iftwo or more microbicidal metals are used, their sum is preferably withinthe ranges set forth above. The term "anhydrous" state means a statebeing free from crystal water, i.e., a state that Z=0 in a formula suchas

    xM.sub.2/n.Al.sub.2 O.sub.3.ySiO.sub.2.zH.sub.2 O

The present invention also provides an antimicrobial polymer compositionthat is chiefly composed of a polymer and the antimicrobial compositiondescribed above. A detailed discussion of this polymer composition isgiven below.

Both halogenated and non-halogenated organic polymers may be used inpreparing the antimicrobial polymer composition of the presentinvention. Non-halogenated organic polymers may be synthetic orsemi-synthetic and include, but not limited to, the following:

Thermoplastic synthetic polymers such as polyethylene, polypropylene,polystyrene, polyamide, polyesters, polyvinyl alcohol, polycarbonates,polyacetals, ABS resins, acrylic resins, fluorine resins, polyurethaneelastomers and polyester elastomers; thermosetting synthetic polymerssuch as phenolic resins, urea resins, melamine resins, unsaturatedpolyester resins, epoxy resins and urethane resins; and regenerated orsemi-synthetic polymers such as rayon, cuprammonium rayon, cellulosemonoacetate, cellulose diacetate and cellulose triacetate. If a strongantimicrobial and/or microbicidal effect is necessary, the polymercomposition is preferably foamed or otherwise shaped into a net, afiber, etc. Preferred from this viewpoint are organic or fiber-formingpolymers such as synthetic polymers exemplified by nylon 6, nylon 66,polyvinyl alcohol, polyethylene terephthalate, polybutyleneterephthalate, polyacrylonitrile, polyethylene, polypropylene andcopolymers thereof, and regenerated or semi-synthetic polymersexemplified by rayon, cuprammonium rayon, cellulose monoacetate,cellulose diacetate and cellulose triacetate. Halogenated organicpolymers that can be used in the present invention also are not limitedto any particular kinds and may be exemplified by polyvinyl chloride andpolyvinylidene chloride.

The time at which the silica gel based antimicrobial composition isadded to the polymer and the method by which it is added are not limitedin any particular way in the present invention. For example, theantimicrobial composition may be mixed with a starting monomer and themixture is then polymerized. In another method, the composition may bemixed with a reaction intermediate and the mixture is then polymerized.Alternatively, the composition may be mixed with the completed polymer,if desired, the silica gel based antimicrobial is mixed with polymerpellets or a master batch is prepared from a polymer containing saidcomposition and the mixture or master batch is shaped to a desired form.In still another method, the antimicrobial composition is mixed with amolding dope, for example, a spinning solution. The procedure of thesemethods is hereinafter referred to simply as "mixing the silica gelbased antimicrobial composition with a polymer of adding it to thepolymer". A suitable method may be adopted taking into account thecharacteristics of the polymer used and process conditions. In ordinarycases, the silica gel based composition is desirably mixed with thepolymer just before molding. However, in order to insure more efficientdispersion of the silica gel based antimicrobial composition, it may bemixed with a monomer. Prior to addition to a polymer, the antimicrobialcomposition may advantageously be dried or heat-treated as alreadymentioned hereinabove. When a predetermined amount of the antimicrobialcomposition is to be added to a polymer, the atmosphere (e.g. anoxidizing atmosphere such as the air or an inert gas atmosphere such asN₂ or CO₂), the temperature for mixing or the mixing time may be held atpreferred conditions in accordance with the specific characteristics ofthe polymer used. The silica gel based antimicrobial composition ispreferably used in an amount of 0.01-20 wt % of the total weight of thepolymer composition. If the content of the silica gel based compositionis less than 0.01 wt % of the total weight of the polymer composition,the antimicrobial and/or microbicidal activity of the polymercomposition is often unsatisfactory against common bacteria and fungi.If the content of the silica gel based composition is more that 20 wt %of the total weight of the polymer composition, the antimicrobial and/ormicrobicidal activity of the resulting polymer composition is saturatedand any further addition of the silica gel based composition will notcontribute to an improved antimicrobial and/or microbicidal action.Furthermore, excessive addition of the silica gel based composition hasthe potential to deteriorate the physical properties of the finallyobtained polymer compsition.

The particle size of the silica gel based antimicrobial composition thatis advantageously used to produce the antimicrobial polymer compositionof the present invention is discussed below. While there is noparticular limitation on the particle size of said composition, there isof course a preferred range depending on the specific use of the finalproduct. For example, particles of the antimicrobial composition withsizes of 30-100 mesh can be used for mixing with the polymer but inorder to insure more uniform dispersion in the polymer, smallerparticles, for example, those having sizes of 200-300 mesh or much finerparticles with sizes of from several microns to less than a hundredmicrons, may be used.

The particle size of the antimicrobial composition may be adjusted byselecting the particle size of the starting silica gel or by pulverizingthe prepared silica gel based antimicrobial composition with a mill thatis selected as appropriate for a specific purpose. When theantimicrobial polymer composition of the present invention is a shapedpart having a certain thickness, for example, in the case where it is tobe applied to various types of containers, pipes, granules of filamentsof large denier, the silica gel based antimicrobial composition may haveparticle sizes of up to less than a hundred to less than a thousandmicrons or even more. If, on the other hand, the polymer composition isto be shaped into fibers of fine denier or thin films, the particle sizeof the silica gel based antimicrobial composition is desirably small.For example, in the case of manufacturing fibers for apparel, particlesizes of not more than 6 microns are preferred.

In addition to the silica gel based antimicrobial composition, theantimicrobial polymer composition of the present invention may containother ingredients that are commonly used in the art. Examples of suchsecondary ingredients include: polymerization catalysts, stabilizers,weathering (lightfast) agents, compounding agents, antioxidants,activators, matting agents, foaming agents, flame retardants, modifiers,brighteners, pigments (colorants), inorganic or organic fillers, variousplasticizers, and lubricants. These additives may be incorporated asrequired. The antibacterial polymer composition of the present inventionmay also contain liquids or organic solvents. When said composition isto be used as a shaped part, its shape and size are in no way limited.In order to provide the shaped part with an antimicrobial and/ormicrobicidal activity, it may be imparted to the whole part of thepolymer, or if desired, to only part thereof. When the microbicidalpolymer composition of the present invention is shaped part, itsmicrobicidal action is considered to be largely dependent on the silicagel based antimicrobial composition present near the surface of theshaped part, so it may be advisable to provide the shaped part with amultilayer structure and treat its outer layer to acquire a microbicidalactivity. In the case of fibers, a core/sheath yarn may be prepared by aknown conjugate fiber spinning technique, with the antimicrobial polymercomposition of the present invention being used as the sheath component.

The present invention further provides an antimicrobial composition foruse in aqueous systems that comprised silica gel having on its surface acoat of aluminosilicate containing at least one microbicidal metal ionselected from the group consisting of silver and zinc. Thisantimicrobial composition has been proposed with a view to improving theknown microbicides for use in aqueous systems. This antimicrobialcomposition has the following two major advantages: there is noparticular need to shape this composition in the manner described inconnection with the antimicrobial zeolite; it can be easily shaped ingranules of various sizes (large, medium and small) spherical beads andother forms by selecting the shape of the starting silica gel inaccordance with a specific object. Further, the antimicrobialcomposition of the present invention for use in aqueous systems has byfar greater mechanical strength and water resistance than the shapedpart of known antimicrobial zeolites, and it will not readilydisintegrate into fine particles in water and hence withstand prolongeduse in aqueous systems. As a further advantage, the antimicrobial and/ormicrobicidal activity of this composition against bacteria and fungi isremarkable and it is capable of inhibiting or killing microorganisms ina shorter time than known antimicrobial zeolites. In other words, themicrobicidal speed of the composition is surprisingly high.

If the composition contains silver as the sole microbicidal metal, itstotal content is preferably at least 0.0003 mmol, more preferably atleast 0.005 mmol, per 100 m² of the surface area of the composition inanhydrous state in order to insure that the composition will exhibitstrong antimicrobial and/or microbicidal action against bacteria andfungi, as well as good antialgal effect. If the composition containsboth silver and zinc as microbicidal metals, the total contents ofsilver and zinc are preferably at least 0.0002 mmol and 0.02 mmol,respectively, per 100 m² of the surface area of the composition inanhydrous state. If the composition contains zinc as the solemicrobicidal metal, its total content is preferably at least 0.08 mmolper 100 m² of the surface area of the composition in anhydrous state. Inorder to insure that the antimicrobial composition of the presentinvention will exhibit satisfactory antimicrobial and/or microbicidaleffect in water over a prolonged time, a predetermined amount of thecomposition may be used after the content of a microbicidal metal ofinterest is adjusted to a value not less than its lower limit specifiedabove in accordance with the quality of water to be treated with thatcomposition. In performing antimicrobial and/or microbicidal treatmenton ordinary aqueous systems, the composition in which the total contentof microbicidal metal is adjusted to lie within the range of 0.0002-0.5mmol per 100 m² of the surface area of the composition in anhydrousstate may be added in the necessary amount as appropriate for thequality of water to be treated.

The antimicrobial composition of the present invention for use inaqueous systems preferably has a pore volume of at least 0.3 cm³ /g anda specific surface area of at least 100 m² /g in order to insure thatsaid composition exhibits satisfactory microbicidal action at anincreased speed.

The silica gel based antimicrobial composition of the present inventionand the antimicrobial polymer composition which uses it have thefollowing features and advantages.

First, silica gel used as the matrix of the antimicrobial composition isporous and the pores in it have an active surface. Hence, chemicalspecies and metal ions will diffuse rapidly during the formation of analuminosilicate coat and ion exchange, whereby the intended chemicalreaction will proceed smoothly to facilitate the production of anantimicrobial composition having desired performance.

The pores in the silica gel based antimicrobial composition of thepresent invention are larger than those in known aluminosilicate basedantimicrobial agents. Hence, microbicidal metal ions formed as a resultof dissociation of the composition will readily diffuse through thepores to have easy access to microorganisms. On the other hand, thepores in known aluminosilicate based antimicrobial compositions, such asantimicrobial zeolites, are so small in size that microbicidal metalions formed as a result of dissociation will diffuse very slowly andsometimes fail to have contact with microorganisms. Hence even if theapparent specific surface area is increased by using porousaluminosilicate particles, the area over which a microbicidal metalmakes effective contact with microorganisms will not increase so much asto enhance their antimicrobial performance to a desired level. This isbecause the effectiveness of the microbicidal metal present on thesurface of the matrix is reduced by "dead spaces" where it is unable tohave contact with microorganisms.

The antimicrobial composition of the present invention does not havethis problem and all microbicidal metals that are present on the surfaceof the matrix work effectively by contacting microorganisms.

Further, the silica gel matrix is covered with an aluminosilicatesubstituted by a microbicidal metal, so the amount of "wasted"microbicidal metal which is occluded within the matrix and henceprevented from contact with microorganisms is substantially reduced.

Because of these two factors, the "effective availability" of themicrobicidal metal, namely, the proportion of the metal used that isoccupied by the metal present on the surface, is markedly increased toinsure that the composition of the present invention need be used in asmaller amount to exhibit satisfactory antimicrobial performance.

Hence, this composition can be mixed with a polymer to produce aneffective antimicrobial polymer composition without causing staining ordiscoloration which would otherwise occur if a microbicidal metal isused in a large amount.

The antimicrobial composition of the present invention has the followingadditional features or advantages. (1) It is totally composed ofinorganic components and the microbicidal metal in it is stably held onthe matrix by ionic bonding. Even if the composition is added or mixedwith a polymer, the release or separation of the microbicidal metal isnegligible. Hence, the antimicrobial polymer based on this compositionhas the advantage that its antimicrobial effect will be sustained for alonger period than that exhibited by polymers containing organicantimicrobial agents. Needless, the evaporation loss of the particles inthe polymer is nil.

(2) The antimicrobial composition of the present invention has notoxicity, is highly safe to the human body and can be handled with greatease.

(3) The antimicrobial composition to be used in the present inventioncan not only be added and mixed with various polymers in an easy way butit can also be dispersed uniformly to provide a homogeneous polymercomposition.

(4) The antimicrobial composition has a stable structure and its heatresisting and weathering properties are excellent. When this compositionis used to prepare a microbicidal polymer, its presence will neitherdeteriorate the physical properties of the polymer nor does it adverselyaffect the heat resistance or weatherability of the polymer composition.

(5) The antimicrobial composition of the present invention has a broadantimicrobial spectrum and proves effective against many bacterial andfungi. It is also anticipated to work as an antialgal agent.

(6) Commercial products of synthetic zeolites contain free alkalies insignificant amounts (pH in 1 g of an aqueous suspension=11.5-12).Antimicrobial zeolites are prepared from these materials by ionexchange. In this case, the free alkalies in the starting zeolite willcause extensive adverse effects on the quality of the antimicrobialzeolite. Thus, it is necessary to adopt an additional step of removingthe free alkalies from zeolite. In contrast, the preparation of theantimicrobial composition to be used in the present invention involves atreatment in a weakly alkaline range as already mentioned above, sothere is no particular need to remove excess alkali. In other words,alkalies do not present any problem in the preparation of thecomposition of the present invention and the finally obtainedcomposition is free from alkalies.

(7) The antimicrobial composition to be used in the present invention isbased on silica gel, so when it is added to or mixed with a polymer, itexhibits not only antimicrobial and/or microbicidal effect but also theinherent action of silica gel as a filler.

(8) The antimicrobial composition of the present invention is useful forthe purpose of providing antimicrobial property for paints, pigments,paper, rubber, etc. Further, the composition has the potential to beused for the purpose of providing antimicrobial and/or microbicidalproperty for various coatings, and for the purpose of providingantimicrobial property for construction materials such as joint fillers,wall materials and tiles. Another potential application of thecomposition is in water treatment.

(9) According to the present invention, polymer compositions can berendered partially or totally resistant to microorganisms. Further, suchantimicrobial polymer compositions have the ability to provideantimicrobial and/or microbicidal property for the atmosphere (gas orliquid phase) with which they make contact.

(10) The antimicrobial polymer composition of the present invention alsohas the potential to be used in applications where deodoring,dehumidification and keeping of freshness are required.

(11) The present invention can be utilized to provide antimicrobialand/or microbicidal property to various polymers including halogenatedand non-halogenated organic polymers. The antimicrobial composition ofthe present invention could be used not only for the purpose ofproviding antimicrobial property for various waxes, paints, pigments,papers, adhesives, coatings and construction materials (e.g. jointfillers, wall materials and tiles) but also in water treatment. Theantimicrobial composition of the present invention can also be used toprovide antimicrobial property for polymer jackets on optical fibers.

(12) The antimicrobial composition of the present invention for use inaqueous systems has high water and wear resistance. Even if it is usedin water, it remains intact for a long time, with only negligibledisintegration into fines.

(13) When the antimicrobial composition of the present invention is usedin water for microbicidal purposes, the microbicidal metal present inpores in silica gel exhibit a very high availability (i.e. thecomposition has a higher efficiency of utilization than knownantimicrobial zeolites).

(14) The antimicrobial composition of the present invention for use inaqueous system is effective not only against common bacterial and fungibut also against algae.

The following examples are provided for the purpose of furtherillustrating the present invention but are in no way to be taken aslimiting.

EXAMPLE 1

This example relates to the preparation of an antimicrobial compositionaccording to the present invention that uses silica gel as a matrix andthat contains silver as a microbicidal metal.

Three liters of desalted water was added to ca. 1.4 kg of crushed silicagel (product of Nishio Kogyo K.K.; specific surface area, 450 m² /g;pore size, 75 Å; pore volume, 0.8 ml/g; particle size, 50-80 mesh). Themixture was stirred at 450-500 rpm to form a homogenous slurry. To theslurry, a 0.5N solution of sodium hydroxide was added slowly until thepH of the slurry was finally adjusted to 9.5-10.0. Then, ca. 63 g ofNaAlO₂ dissolved in 3 l of water was added to the slurry and the mixturewas stirred at 20°-30° C. for ca. 12 hours at 450-500 rpm. Afterstirring, the mixture was filtered and the solid phase was washed withwater to remove excess alkali and unreacted NaAlO₂. During the washing,the pH of the filtrate was held at about 9. To the solid phase, asolution of silver nitrate (aq. sol. containing ca. 0.68M AgNO₃) wasadded and the resulting mixture was stirred continuously at 450-550 rpmover a period of about 7 hours. During the stirring, the mixture washeld at room temperature (20°-21° C.). The above procedure substantiallycompleted the preparation of an antimicrobial composition containingmicrobicidal silver ions. After the end of the reaction, the product wasfiltered and washed to remove excess Ag⁺ from the solid phase. Thewashed product was dried at 100°-110° C. to obtain a silica gel basedantimicrobial composition containing silver as a microbicidal metal.

The antimicrobial composition of the present invention prepared inExample 1 had a specific surface area of 324 m² /g (as measured by N₂gas adsorption in the BET method) and a pore volume of 0.72 cm³ /g. Theamount of silver as determined was 4.90% (on an anhydrous basis). Thecomposition contained 0.14 mmol of silver per 100 m² of the surface areaon an anhydrous basis.

                  TABLE 1                                                         ______________________________________                                        Antimicrobial Composition (Example 1)                                         Specific surface area                                                                        Microbicidal metal (Ag)                                        (m.sup.2 /g)   in mmol/100 m.sup.2                                            ______________________________________                                        324            0.14                                                           ______________________________________                                    

EXAMPLE 2

This example relates to the preparation of an antimicrobial compositionaccording to the present invention that uses silica gel as a matrix andthat contains both silver and zinc as microbicidal metals.

Desalted water (2.5 l) was added to ca. 1.3 kg of spherical silica gelbeads (product of Toyota K.K.; specific surface area, 450 m² /g; poresize, 60 Å; pore volume, 0.75 cm³ /g; particle size; 40 mesh pass). Themixture was stirred at 400-450 rpm to form a homogeneous slurry. To theslurry, a 0.5N solution of sodium hydroxide was added slowly until thepH of the slurry was finally adjusted to 9.5-10.0. Then, ca. 2.6 l of anaqueous solution of sodium aluminate (0.27 mol/l) was added to theslurry, which was stirred at 20°-23° C. for ca. 15 hours at 450-500 rpmto form an aluminosilicate coat on the surfaces of pores in the silicagel. Subsequently, the mixture was filtered and the solid phase waswashed with water to remove excess alkali and unreacted sodiumaluminate. During the washing, the pH of the filtrate was held at ca. 9.A mixture of AgNO₃ and Zn(NO₃)₂ (an aqueous solution of 0.6M AgNO₃ and0.2M Zn(NO₃)₂ ; pH=4.1) was added to the washed solid phase and theresulting mixture was held at 20°-21° C. and stirred continuously at450-500 rpm over a period of ca. 15 hours. By the above procedure of ionexchange reaction, an antimicrobial composition containing silver andzinc as microbicidal metals was prepared. The composition was filteredand washed to remove excess silver and zinc from the solid phase. Thewashed product was dried at 100°-110° C. to prepare a silica gel basedantimicrobial composition containing both silver and zinc asmicrobicidal metals.

The antimicrobial composition of the present invention prepared inExample 2 had a specific surface area of 319 m² /g (as measured by N₂gas adsorption in the BET method) and a pore volume of 0.67 cm³ /g. Theamounts of silver and zinc as determined were 3.79% and 0.83% (on ananhydrous basis). The composition contained silver and zinc in amountsof 0.11 mmol and 0.04 mmol, respectively, per 100 m² of the surface areaon an anhydrous basis.

                  TABLE 2                                                         ______________________________________                                        Antimicrobial Composition (Example 2)                                                            Microbicidal metal                                         Specific surface area                                                                            in mmol/100 m.sup.2                                        (m.sup.2 /g)       Ag     Zn                                                  ______________________________________                                        319                0.11   0.04                                                ______________________________________                                    

In order to compare the antimicrobial activity of the compositionprepared in Example 2 with that of a known antimicrobial zeolite, a testwas conducted under the same conditions according to the "shake flaskmethod" reviewed by the Fibrous Product Sanitary Processing Conference".In the test, Escherichia coli and Staphylococcus aureus were used astest bacteria. The antimicrobial zeolite used as a comparative samplewas dried fine powder of NaAgZnZ (3.97% Ag and 1.27% Zn on an anhydrousbasis; Z=the matrix of zeolite A). The test procedure was as follows.

(a) A suspension (1/15M; pH 7.2) containing ca. 10⁸ cells/ml of a testbacterium was prepared and diluted appropriately for the test.

(b) Test by the shake flask method: The test sample (the dried powder ofknown antimicrobial zeolite or the antimicrobial composition of Example2) was taken in an amount of 0.005 g into a 200-ml volumetric flask. Aphosphate buffer solution and the suspension of test bacterium wereadded to make a total volume of 50 ml, with the number of cells beingadjusted to 10⁶ per ml.

(c) Test bacteria: Escherichia coli (IFO-12734) and Staphylococcusaureus (IFO-12732)

(d) Medium: Mueller Hinton 2 (BBL)

The test results are shown in tables 3 and 4 below, in which the datafor a control containing no antimicrobial agent is also shown.

                  TABLE 3                                                         ______________________________________                                        Comparison of Antimicrobial Activity Between                                  Antimicrobial Zeolite and the Antimicrobial                                   Composition of Example 2 (Test bacterium:                                     E. coli; Initial cell count: 5.6 × 10.sup.6 /ml;                        total liquid volume: 50 ml)                                                                   Anti-    No. of viable cells                                  Antimicrobial   microbial                                                                              per ml                                               agent           metal            30                                           Type     Amount     content  0     10    (min)                                ______________________________________                                        Anti-    5 mg/50 ml Ag =     5.6 ×                                                                         1.1 ×                                                                         0                                    microbial                                                                              (0.1 mg/ml)                                                                              0.20 mg  10.sup.6                                                                            10.sup.6                                   zeolite             Zn =                                                      (NaAgZnZ)           0.06 mg                                                   Anti-    5 mg/50 ml Ag =     5.6 ×                                                                         8.9 ×                                                                         0                                    microbial                                                                              (0.1 mg/ml)                                                                              0.19 mg  10.sup.6                                                                            10.sup.3                                   composition         Zn =                                                      of Example 2        0.04 mg                                                   Control  No Anti-            5.6 ×                                                                         5.4 ×                                                                         5.2 ×                                   microbial           10.sup.6                                                                            10.sup.6                                                                            10.sup.6                                      agent added                                                          ______________________________________                                    

                                      TABLE 4                                     __________________________________________________________________________    Comparison of Antimicrobial Activity Between Antimicrobial Zeolite and        the Antimicrobial Composition of Example 2 (Test bacterium: Staphyl.          aureus;                                                                       Initial cell count: 1.5 × 10.sup.6 /ml; Total liquid volume: 50         ml)                                                                           Antimicrobial agent                                                                         Antimicrobial                                                                         No of viable cells per ml                               Type   Amount metal content                                                                         0    5    10   15   30   120 (min)                      __________________________________________________________________________    Antimicrobial                                                                        5 mg/50 ml                                                                           Ag = 0.20 mg                                                                          1.5 × 10.sup.6                                                               --   --   --   6.8 × 10.sup.6                                                               0                              zeolite                                                                              (0.1 mg/ml)                                                                          Zn = 0.06 mg                                                    (NaAgZnZ)                                                                     Antimicrobial                                                                        5 mg/50 ml                                                                           Ag = 0.19 mg                                                                          1.5 × 10.sup.6                                                               4.1 × 10.sup.3                                                               5.2 × 10                                                                     0    0    0                              composition                                                                          (0.1 mg/ml)                                                                          Zn = 0.04 mg                                                    of Example 2                                                                  Control                                                                              No antimicrobial                                                                             1.5 × 10.sup.6                                                               1.2 × 10.sup.6                                                               1.3 × 10.sup.6                                                               1.2 × 10.sup.6                                                               1.3 × 10.sup.6                                                               1.2 × 10.sup.6                  agent added                                                            __________________________________________________________________________

Each of the antimicrobial zeolite and the antimicrobial composition ofExample 2 which were subjected to the antimicrobial activity test underdiscussion contained both silver and zinc as microbicidal metals and theformer contained these metals in slightly larger amounts than thelatter. However, as Table 3 shows, the antimicrobial composition of thepresent invention exhibited greater antimicrobial activity againstEscherichia coli in view of the high rate at which the number of cellsdecreased with time. After the passage of 10 minutes, the cell count inthe suspension containing the antimicrobial zeolite was 1.1×10⁶ per ml(death rate, 80.36%) but the number of viable cells in the suspensioncontaining the antimicrobial composition of Example 2 decreased to amuch smaller level of 8.9×10³ /ml (death rate, 99.84%).

In the test using Staphylococcus aureus (see Table 4), the number ofviable cells in the suspension containing antimicrobial zeolite was6.8×10⁴ /ml after the passage of 30 minutes and the death rate was95.47%. On the other hand, the viable cell count in the suspensioncontaining the antimicrobial composition of Example 2 was 5.2×10/ml at10 minutes and almost all cells had been killed. After the passage of 15minutes, the death rate was 100%. Table 4 clearly shows that theattenuation rate of Staphylococcus aureus was by far faster when theantimicrobial composition of the present invention than when the knownantimicrobial zeolite was used.

The results of the antimicrobial activity test revealed that theantimicrobial composition of the present invention is superior to theknown antimicrobial zeolite in antimicrobial action. This is animportant point worth particular mention. The difference between the twoantimicrobial agents in antimicrobial and/or microbicidal effect wouldoriginate from their essential structural difference. The antimicrobialcomposition of the present invention has a silicon-oxgen skeletalstructure based on amorphous silica gel whereas the known antimicrobialzeolite is crystalline and has a silicon-oxygen-aluminum skeletalstructure. Because of this obvious structural difference, the twoantimicrobial agents will unavoidably differ in physical properties. Forexample, both agents are porous but the size of pores in the matrix ismuch greater in the antimicrobial composition of the present inventionthan in the antimicrobial zeolite. There is another difference and thatis in the distribution of bactericidal metals. In the composition of thepresent invention, microbicidal metals are distributed on the surface ofpores, substantially by ionic bonding. On the other hand, in the knownantimicrobial zeolite, microbicidal metals are distributed uniformly inthe zeolite matrix. When this structural difference is taken intoaccount together with the arrival of microorganisms through diffusion atthe active sites where microbicidal metals are coordinated and the areaof contact between the microorganism and microbicidal metal, thecomposition of the present invention is by far advantageous over theknown antimicrobial zeolite. In addition, the efficiency of utilizationof microbicidal metals for antimicrobial and/or microbicidal purposes ishigher in the composition of the present invention than in the knownantimicrobial zeolite. The pores present in the matrix of the knownantimicrobial zeolite have such a small size that depending on the kindof microorganisms, the diffusion rate will decrease. Further,microbicidal metal ions formed as a result of dissociation will diffuseso slowly that an unduly long time is taken for those metal ions tocontact microorganisms or, in an extreme case, such contact is entirelyimpossible. These phenomena will contribute to a lower efficiency ofutilization of microbicidal metals in the antimicrobial zeolite.

EXAMPLE 3

This example relates to the preparation of an antimicrobial compositionaccording to the present invention that uses silica gel as a matrix andthat contains copper as a microbicidal metal.

Desalted water (1.7 l) was added to ca. 0.9 kg of silica gel (ID silicagel of Nishio Kogyo K.K.; specific surface area, 310 m² /g; pore size,150 Å; pore volume, 1.2 ml/g; particle size, 50-80 mesh). The mixturewas stirred at 450-500 rpm to form a homogeneous slurry. To the slurry,a 0.5N sodium hydroxide solution was slowly added until the pH of theslurry was finally adjusted to 9.5-10.0. Then, an aqueous solution ofsodium aluminate prepared by dissolving ca. 100 g of NaAlO₂ in 1.8 l ofwater was added to the slurry, which was stirred at 30°-32° C. for ca.16 hours at 450-500 rpm. After these treatments, the silica gel waspacked in an ion-exchange column having an inside diameter of 50 mm andwashed with water at a flow rate of 4-5 ml/min to remove excess alkaliand unreacted NaAlO₂, with the pH of the effluent from the washed columnbeing held at 9. Subsequently, the packing in the column was treatedwith an excess aqueous solution of cupric nitrate (pH 4.0). Stated morespecifically, the column packing was treated with an aqueous solution ofCu(NO₃)₂ containing 2.5-3 equivalents of Na⁺ in the NaAlO₂ solution. Theliquid temperature was 20°-22° C. and the flow rate was 3-4 ml/min.After the ion exchange, the column packing was washed with water at aflow rate of 4-5 ml/min to remove excess Cu²⁺ from the solid phase.After the washing, the column packing was recovered and dried at100°-110° C. to prepare a silica gel based antimicrobial compositioncontaining copper as a microbicidal metal.

The antimicrobial composition of the present invention prepared inExample 3 had a specific surface area of 248 m² /g (as measured by N₂gas adsorption in the BET method) and a pore volume of 1.04 cm³ /g. Theamount of copper as determined was 4.25% (on an anhydrous basis). Thecomposition contained copper in an amount of 0.27 mmol per 100 m² of thesurface area on an anhydrous basis.

                  TABLE 5                                                         ______________________________________                                        Antimicrobial Composition (Example 3)                                         Specific surface area                                                                        Microbicidal metal (Cu)                                        (m.sup.2 /g)   in mmol/100 m.sup.2                                            ______________________________________                                        248            0.27                                                           ______________________________________                                    

The antimicrobial power of the silica gel based compositions of thepresent invention is discussed below.

Inhibition Zone Formation Test

An inhibition zone formation test was conducted by the method summarizedbelow.

(1) The test sample (the dried product of the antimicrobial compositionprepared in Example 1 or 2) was suspended at a concentration of 100mg/ml and impregnated in a disk.

(2) For the growth of bacteria, a Mueller Hinton medium was used, andfor the growth of fungi, a Sabouraud's agar medium was used.

(3) The test microorganism was suspended in physiological saline at aconcentration of 10⁸ cells/ml and 0.1 ml of the suspension was dispersedin the media with a Conradi's rod.

(4) The disk impregnated with the test sample was plated on the media.

(5) As for the bacteria. the disks were checked for the formation of aninhibition zone after the passage of 18 hours at 37° C. As for thefungi, the disks were checked for the formation of an inhibition zoneafter the passage of one week at 30° C. The results are shown in Table 6below.

                  TABLE 6                                                         ______________________________________                                        Evaluation of Antimicrobial Activity                                          (Inhibition Zone Formation)                                                                                    Silica Gel                                   Antimicrobial                    (starting                                    composition                      material used                                Microorganism                                                                            Example 1  Example 2  in Example 1                                 ______________________________________                                        Eschirichia                                                                              +          +          -                                            coli                                                                          Staphylococcus                                                                           +          +          -                                            aureus                                                                        Pseudomonas                                                                              +          +          -                                            aeruginosa                                                                    Aspergillus                                                                              +          +          -                                            flavus                                                                        Aspergilus +          +          -                                            niger                                                                         ______________________________________                                         +: Inhibition zone formed                                                     -: No Inhibition zone formed                                             

The antimicrobial composition prepared in Example 1 which contained Agas a microbicidal metal and the antimicrobial composition prepared inExample 2 which contained both Ag and Zn as microbicidal metals wereeffective against both bacterial Escherichia coli, Staphylococcus aureusand Pseudomonas aeruginosa and fungal Asperigillus flavus andAspergillus niger, forming an inhibition zone in all of these fivecases. The "silica gel" mentioned in Table 6 was the silica gel used asthe starting material in the preparation of the antimicrobialcomposition in Example 1. Having no antimicrobial activity, this silicagel did not form any inhibition zone as indicated in Table 6.

Death Rate Measurement

One milliliter of a suspension containing 10⁵ /ml of spores ofAspergillus niger or Aspergillus flavus was injected and mixed with 9 mlof a suspension of the test sample (the dried product of theantimicrobial composition prepared in Example 1, 2 or 3) at aconcentration of 500 mg/ml and the mixture was left to stand at 30° C.for 24 hours. A portion (0.1 ml) of the mixture was dispersed in aSabouraud's agar medium and cultured at 30° C. for 48 hours. The numberof viable cells was counted to determine the death rate of each fungus.The results are shown in Table 7.

                  TABLE 7                                                         ______________________________________                                        Measurement of Death Rate                                                     Antimicrobial                                                                             Death Rate (%)                                                    composition Aspergillus flavus                                                                         Aspergillus niger                                    ______________________________________                                        Example - 1 100          100                                                  Example - 2 100          100                                                  Example - 3  96           81                                                  ______________________________________                                    

The antimicrobial compositions prepared in Examples 1 and 2 had a 100%death rate for Aspergillus flavus and Aspergillus niger, indicating thestrong fungicidal action of the compositions. The antimicrobialcomposition prepared in Example 3 also had good antifungal effect asalready demonstrated in Example 3.

Method of Testing Antimicrobial Activity in Examples 4-8 and ComparativeExample

Additional samples were prepared in Examples 4-8 and Comparative Exampleand their performance was evaluated by an antimicrobial activity test inthe manner to be described below. When the test samples were shaped in aplate, film or sheet form, the test was conducted by spraying, whereasthe samples in the form of monofilaments were tested by the "shake flaskmethod" specified by the Fibrous Product Sanitary Processing Conference.

(I) Preparation of a cell suspension of bacterium:

The cells of a test bacterium that had been cultivated in a common agarmedium at 37° C. for 18 hours were suspended in a phosphate buffer(1/15M; pH 7.2) at a concentration of 10⁸ cells/ml and diluted asappropriate for the test.

(II) Preparation of a cell suspension of fungus:

Conidia of a test fungus that had been cultivated on a slant potatodextrose agar medium at 25° C. for 7 days were suspended inphysiological saline containing sterile 0.05% polysorbate to prepare asuspension at a concentration of 10⁷ cells/ml, which was diluted asappropriate for the test.

(III) Antimicrobial activity test by the spray method:

The surface of a test piece (50×50×ca. 1.5 mm except for a film whichwas 30 μm thick) cleaned with alcohol-impregnated absorbent wadding wassprayed with a predetermined amount of cell suspension and stored at 35°C. for a predetermined time. Before measurement, the cells on the testpiece were washed off and the number of cells in the washings wascounted.

(IV) Antimicrobial activity test by the shake flask method:

One gram of a test piece (monofilament) was put into a 200-ml volumetricconical flask containing 70 ml of a phosphate buffer. The flask wasfurther charged with a suspension of test microorganism at aconcentration of 10⁴ cells/ml and shaken at 25°±5° C. and the number ofviable cells was counted at given time intervals.

(V) Test microorganism:

Staphylococcus aureus IFO-12732

Escherichia coli IFO-12734

Aspergillus niger IFO-31125

(VI) Medium (for counting viable cells): Muller hinton 2 (BBL) forbacteria, and Sobouraud's dextrose agar (BBL) for fungus

EXAMPLE 4

This example relates to the preparation of a shaped part ofpolyvinylidene chloride (PVDC) containing an antibacterial compositionhaving silver supported as a microbicidal metal, as well as theevaluation of its antimicrobial activity.

The dried product of the antimicrobial composition containing silver asa microbicidal metal which was prepared in Example 1 (Ag=0.14 mmol per100 m² /g of the surface area in anhydrous state; specific surface area,324 m² /g as measured by N₂ adsorption in the BET method) was groundinto fine particles and heated at 190°-200° C. under vacuum to a watercontent of 2% and below. The dried fine particles were mixed with PVDC,with the former being in an amount of 1.5% or 3%. The mixtures were thenheated close to 180° C., homogenized at the same temperature, andpressed at ca. 20 kg/cm².G to form parts measuring ca. 100×100×1.5 mm.Each of the shaped parts was cut into small test pieces (ca. 50×50×1.5mm). The thus prepared test pieces were designated PVDC-1 and PVDC-2. Asa comparison, a shaped part of PVDC (ca. 100×100×1.5 mm) containing noantimicrobial composition was prepared for use in a blank test. This wascut into small test pieces (PVDC-BL; ca. 50×50×1.5 mm). All of the testpieces were subjected to an antimicrobial activity test by the spraymethod and the results were as shown in Table 8.

                  TABLE 8                                                         ______________________________________                                        Antimicrobial Activity Test by                                                the Spray Method (Example 4)                                                         Content of                                                                    antimicrobial             No. of viable                                       composition in            cells per sample                             Test   polymer com-                                                                              Micro-                12                                   sample position (%)                                                                              organism  0     5     (hr)                                 ______________________________________                                        PVDC-1   1.5       Escherichia                                                                             8.7 ×                                                                         0     0                                                       coli      10.sup.6                                         PVDC-2 3           Escherichia                                                                             8.9 ×                                                                         0     0                                                       coli      10.sup.6                                         PVDC-  --          Escherichia                                                                             9.2 ×                                                                         8.8 ×                                                                         8.3 ×                          BL                 coli      10.sup.6                                                                            10.sup.6                                                                            10.sup.6                             PVDC-2 3           Aspergillus                                                                             5.8 ×                                                                         7.6 ×                                                                         0                                                       niger     10.sup.6                                                                            10                                         PVDC-  --          Aspergillus                                                                             6.1 ×                                                                         5.7 ×                                                                         5.4 ×                          BL                 niger     10.sup.6                                                                            10.sup.6                                                                            10.sup.6                             ______________________________________                                    

The PVDC polymer compositions containing 1.5% and 3%, respectively, ofthe antimicrobial composition (PVDC-1 and PVDC-2) had strongantimicrobial activity against Escherichia coli and all cells were foundto be dead after the passage of 5 hours. As Table 8 shows, PVDC-BL(blank test sample) did not exhibit any antimicrobial activity at all.In the test on fungal Aspergillus niger, PVDC-2 reduced the cell countto 7.6×10 per sample at 5 hours, which was equivalent to a death rate ofat least 99.99%. On the other hand, PVDC-BL (blank test sample) had noantimicrobial activity at all. The above test results clearly show thatthe antimicrobial polymer compositions of the present invention havesatisfactory antimicrobial and/or microbicidal activity.

EXAMPLE 5

This example relates to the preparation of a shaped polyvinyl chloride(PVC) containing an antimicrobial composition having silver as amicrobicidal metal, as well as the evaluation of its antimicrobialactivity.

The dried product of the antimicrobial composition containing silver asa microbicidal metal which was prepared in Example 1 (Ag=0.14 mmol per100 m² of the surface area in anhydrous state; specific surface area,324 m² /g as measured by N₂ adsorption in the BET method) was groundinto fine particles and heated at 200°-210° C. under vacuum to a watercontent of 1.5% and below. The dried fine particles were mixed with PVCand the blend was shaped into PVC sheets by the following procedure.Fifty parts of a plasticizer (DOP) was added to 100 parts of PVC("Nippolit SL" of general-purpose grade of Chisso Corporation; degree ofpolymerization, 1,000); after adding a stabilizer and a gelationaccelerator in small amounts, the previously prepared fine particulateantimicrobial composition was added in such an amount that it wouldassume 2 or 3% of the resulting mixture. The mixtures were then heatedat 140°-150° C. and homogenized by kneading on mixing rolls. Thehomogenized mixtures were shaped into sheets of a thickness of ca. 1.5mm.

The shaped PVC was cut into small test pieces (ca. 50×50×1.5 mm) thatwere respectively designated PVC-1 and PVC-2. These samples weresubjected to an antimicrobial activity test by the spray method. As acomparison, a PVC sheet containing no antimicrobial composition wasprepared for use in a blank test in accordance with the method ofpreparing the above-described antimicrobial PVC sheets. This PVC sheetwas cut into small test pieces, designated PVC-BL (ca. 50×50×1.5 mm). Itwas also subjected to an antimicrobial activity test by the spraymethod. The results are shown in Table 9 below.

                  TABLE 9                                                         ______________________________________                                        Antimicrobial Activity Test by                                                the Spray Method (Example 5)                                                  Content of                                                                    antimicrobial            No. of viable                                        composition in           cells per sample                                     Test  polymer com-                                                                              Micro-                 24                                   sample                                                                              position (%)                                                                              organism   0     6     (hr)                                 ______________________________________                                        PVC-1 2           Staphylo-  3.9 ×                                                                         0     0                                                      coccus aureus                                                                            10.sup.6                                         PVC-2 3           Staphylo-  4.1 ×                                                                         0     0                                                      coccus aureus                                                                            10.sup.6                                         PVC-  --          Staphylo-  3.6 ×                                                                         1.8 ×                                                                         1.1 ×                          BL                coccus aureus                                                                            10.sup.6                                                                            10.sup.6                                                                            10.sup.6                             ______________________________________                                    

PVC-1 and PVC-2 which contained the antimicrobial composition inrespective amounts of 2% and 3% were found to have killed all cells(cell count=0) at 6 hours. PVC-BL, the sample for the blank test, wasnot at all effective against the test microorganisms. The above resultsclearly show that the PVC polymer compositions containing theantimicrobial composition of the present invention exhibit remarkablemicrobicidal activity.

EXAMPLE 6

This example relates to the preparation of a PP (polypropylene) filmcontaining an antimicrobial composition having both silver and zinc asmicrobicidal metals.

The dried product of the antimicrobial composition containing silver andzinc as microbicidal metals which was prepared in Example 2 (0.11 mmolAg and 0.04 mmol Zn per 100 m² of the surface are an anhydrous state;specific surface area, 319 m² /g as measured by N₂ adsorption in the BETmethod) was ground into fine particles and heated at ca. 200° C. undervacuum to a water content of 1.5% and below. The dried fine particles ofthe antimicrobial composition were mixed with PP (A4141 of ChissoCorporation) in such an amount that the former would assume 1.5% or 2.5%of the resulting mixture. The mixtures were then shaped into films 30 μmthick by inflation molding with the cylinder and die outlet being heldat temperatures of 210°-220° C. and ca. 220° C., respectively, and withthe screw rotating at 25 rpm. The resulting PP films were cut into smalltest pieces (PP-1 and PP-2 each measuring ca. 50 mm×50 mm×30 μm), whichwere subjected to an antimicrobial activity test. As a comparison, a PPfilm (30 μm thick) containing no antimicrobial composition was preparedas already described for use in a blank test. This film was cut intosmall test pieces (ca. 50 mm×50 mm×30 μm), designated PP-BL, andsubjected to an antimicrobial test. The results are shown in Table 10below.

                  TABLE 10                                                        ______________________________________                                        Antimicrobial Activity Test by                                                the Spray Method (Example 6)                                                  Content of                                                                    antimicrobial            No. of viable                                        composition in           cells per sample                                     Test  polymer com-                                                                              Micro-                 24                                   sample                                                                              position (%)                                                                              organism   0     12    (hr)                                 ______________________________________                                        PP-1  1.5         Staphylo-  7.3 ×                                                                         0     0                                                      coccus aureus                                                                            10.sup.6                                         PP-2  2.5         Staphylo-  7.6 ×                                                                         0     0                                                      coccus aureus                                                                            10.sup.6                                         PP-BL --          Staphylo-  7.9 ×                                                                         5.1 ×                                                                         3.9 ×                                            coccus aureus                                                                            10.sup.6                                                                            10.sup.6                                                                            10.sup.6                             ______________________________________                                    

When PP-1 and PP-2 films containing the antimicrobial composition ofExample 2 respective amounts of 1.5% and 2% were used, the cell count ofStaphylococcus aureus was zero at 12 hours, indicating the strongbactericidal activity of these samples. On the other hand, PP-BL film asthe blank test sample was not at all effective against Staphylococcusaureus. These results clearly show that the PP polymer composition infilm form which contained the antimicrobial composition of the presentinvention exhibit remarkable microbicidal activity.

EXAMPLE 7

This example relates to the preparation of HDPE (high-densitypolyethylene) monofilaments containing an antimicrobial compositionhaving both silver and zinc as microbicidal metals.

The HDPE used in Example 7 was "Showrex F 5012M" having melt index(M.I.) of 1.2. The dried product of the antimicrobial compositioncontaining silver and zinc as microbicidal metals which was prepared inExample 2 (0.11 mmol Ag and 0.04 mmol Zn per 100 m² of the surface areain anhydrous state; specific surface area, 319 m² /g by N₂ adsorption inthe BET method) was ground with a jet mill to fine particles having anaverage size of 15 μm. These particles were heated at ca. 210° C. undervacuum to a water content of 1.5% and below. The dried fine particles ofthe antimicrobial composition were mixed with HDPE in such an amountthat the former would assume 1.5% or 3% of the resulting mixture on adry basis. The mixtures were then shaped into HDPE monofilaments of anantimicrobial polymer composition by extrusion molding under thefollowing conditions: temperature, 225°±5° C.; pressure, ca. 100kg/cm².G; residence time, 10-12 minutes; throughput, 1.5 kg/hr; screwrotating speed, 20 rpm; length (L) to diameter (D) ratio of screw,L/D≃25. The monofilaments were drawn at a ratio of ca. 10 to a finenessof ca. 400 denier. The resulting monofilaments were designated HDPE-1and HDPE-2.

These monofilaments (ca. 400 d) had satisfactory strength. A portion (1g) of them was subjected to an antimicrobial activity test by the shakeflask method already described herein. The results are shown in Table 11below.

                  TABLE 11                                                        ______________________________________                                        Antimicrobial Activity Test by                                                Shake Flask Method (Example 7)                                                Content of                                                                    antimicrobial            No of viable                                         composition in           cells per sample                                     Test   polymer com-                                                                              Micro-                24                                   sample position (%)                                                                              organism  0     6     (hr)                                 ______________________________________                                        HDPE-1 1.5         Escherichia                                                                             5.3 ×                                                                         0     0                                                       coli      10.sup.4                                         HDPE-2 3           Escherichia                                                                             7.8 ×                                                                         0     0                                                       coli      10.sup.4                                         HDPE-  --          Escherichia                                                                             7.3 ×                                                                         7.0 ×                                                                         6.8 ×                          BL                 coli      10.sup.4                                                                            10.sup.4                                                                            10.sup.4                             HDPE-2 3           Aspergillus                                                                             3.9 ×                                                                         5.4 ×                                                                         0                                                       niger     10.sup.4                                                                            10                                         HDPE-  --          Aspergillus                                                                             3.4 ×                                                                         3.1 ×                                                                         2.6 ×                          BL                 niger     10.sup.4                                                                            10.sup.4                                                                            10.sup.4                             ______________________________________                                    

When HDPE-1 and HDPE-2 monofilaments containing the antimicrobialcomposition of Example 2 in respective amount of 1.5% and 3% were used,the cell count of bacterial Escherichia coli was zero at 6 hours,indicating the strong bactericidal activity of these samples. On theother hand, HDPE-BL as the blank test sample containing no antimicrobialcomposition was not at all effective against Escherichia coli. WhenHDPE-2 monofilaments containing said antimicrobial composition in anamount of 3% was used, the cell count of fungal Aspergillus niger was5.4×10 cells per ml at 6 hours, which was equivalent to a death rate of99.9%. When 24 hours passed, all cells were found dead. On the otherhand, HDPE-BL monofilaments as the blank test sample were not at alleffective against Aspergillus niger. These results clearly show that theHDPE monofilaments containing the antimicrobial composition of thepresent invention exhibit strong microbicidal action.

EXAMPLE 8

This example relates to the preparation of a shaped part of PS(polystyrene) containing an antimicrobial composition having silversupported as a microbicidal metal, as well as the evaluation of itsantimicrobial activity.

The dried product of the antimicrobial composition containing silver asa microbicidal metal which was prepared in Example 1 (Ag=0.14 mml per100 m² of the surface area in anhydrous state; specific surface area,324 m² /g as measured by N₂ adsorption in the BET method) was groundinto fine particles and heated at 200°-210° C. under vacuum to a watercontent of 1.5% and below. The dried fine particles were mixed with PSand a shaped PS part having a thickness of ca. 1.5 mm was prepared bythe following procedure. The fine particles of the antimicrobialcomposition were added to PS ("Denka Styrol GD-1-301") in such an amountthat the former would assume 0.70% of the resulting mixture. The mixturewas then heated to 165°-170° C. and melted at the same temperature in akneader. The melt was subsequently extrusion molded to a part having athickness of ca. 1.5 mm. The shaped part was cut into small test pieces,PS-1, measuring ca. 50 mm×50 mm×1.5 mm. As a comparison, small testpieces, PS-BL (ca. 50 mm×50 mm×1.5 mm), containing no antimicrobialcomposition were prepared by the same procedure of molding for use in ablank test. The test results are shown in Table 12 below.

                                      TABLE 12                                    __________________________________________________________________________    Antimicrobial Activity Test by the Spray Method (Example 8)                   Test                                                                              Type and Amount of  No. of viable cells per sample                        sample                                                                            microbicidal agent (%)                                                                    Microorganism                                                                         0   6     12   48 (hr)                                __________________________________________________________________________    PS-1                                                                              microbicidal solid                                                                        Escherichia coli                                                                      5.5 × 10.sup.5                                                               1.2 × 10.sup.2                                                               0    0                                          particles, 0.70%                                                          PS-BL                                                                               --        Escherichia coli                                                                      5.3 × 10.sup.5                                                               5.0 × 10.sup.5                                                               4.7 × 10.sup.5                                                               4.1 × 10.sup.5                   PS-2*                                                                             antimicrobial                                                                              Escherichia coli                                                                     5.1 × 10.sup.5                                                               7.6 × 10.sup.4                                                               5.8 × 10.sup.2                                                               0                                          zeolite, 1.0%                                                             __________________________________________________________________________     *Comparative Example                                                     

COMPARATIVE EXAMPLE

In this comparative example, a shaped PS part (1.5 mm thick) containing1.0% NaAgZ (the formula for antimicrobial zeolite, in which Ag=3.95% ona dry basis, and Z represents the matrix of zeolite A was prepared usingthe fine powder of NaAgZ and PS (the same as used in Example 8) by amethod that was identical to that used in Example 8. The shaped part wascut into small test pieces, PS-2 (ca. 50 mm×50 mm×1.5 mm), for use as acomparison which was subjected to an antimicrobial activity test underthe same conditions as adopted in Example 8. The results are also shownin table 12.

As Table 12 shows, the sample PS-1 (Example 8) containing 0.70% of theantimicrobial composition of the present invention exhibited strongbactericidal activity against Escherichia coli and its cell countdropped to 1.2×10² per sample at 6 hours, which was equivalent to adeath rate of 99.98%. At 12 hours, all cells of Escherichia coli werefound dead. In contrast, the PS-BL sample (for use in blank test)containing no antimicrobial composition was not at all effective againstEscherichia coli. The PS-2 sample (Comparative Sample) containing 1.0%antimicrobial zeolite exhibited microbicidal action against Escherichiacoli and its cell count was 7.6×10⁴ and 5.8×10² per sample at 6 hoursand 12 hours, respectively. The former value was equivalent to a deathrate of 85.1% and the latter to 99.9%. Comparing the cell count profilesof PS-1 and PS-2, one can readily see that the former sample exhibitedstronger bactericidal activity than the latter.

PS-1 (Example 8) containing 0.7% of the antimicrobial composition of thepresent invention had a Ag content of 0.034%, whereas PS-2 (ComparativeSample) containing 1.0% of antimicrobial zeolite had a Ag content of0.039%. PS-2 contained silver in a slightly larger amount than PS-1 andyet, from the viewpoint of antimicrobial efficacy, PS-1 was superior toPS-2.

This difference in antimicrobial effect would have resulted from theessential structural difference between the antimicrobial composition ofthe present invention and the antimicrobial zeolite that were added tothe polymer. For example, the differences in the pores in the matrix andthe distribution of microbicidal metals result in the differences inantimicrobial effect between the two samples (see the previousdiscussion of the features and advantages of the polymer compositioncontaining the antimicrobial composition of the present invention). Asalready mentioned, the PS sample containing the antimicrobialcomposition used in Example 8 had a silver content of 0.034%. Silver inthe antimicrobial composition used in the antimicrobial activity testwas not distributed uniformly in the silica gel matrix but distributedon the surfaces of great many pores in the silica gel (which were muchlarger than the pores in antimicrobial zeolite) by ionic bonding, withthe Ag content amounting to 0.14 mmol/100 m². On the other hand, NaAgZ(pore size, 4 Å) used as the comparative example contained 0.039% Ag inPS. In sharp contrast from the antimicrobial composition used in Example8, the comparative NaAgZ had Ag distributed uniformly in the zeolitematrix. The silver content in the polymer was 0.034% in Example 8 and itwas distributed on the active surfaces of pores in silica gel. On theother hand, the silver content of the polymer in the comparative samplewas 0.039% which differed from the silver content of the sample ofExample 8 only slightly. However, as already mentioned, the silver inthe antimicrobial composition used in Example 8 was distributed only onthe active surfaces of pores in silica gel, so the amount effectivesilver available for microbicidal purposes was greater than that ofsilver in NaAgZ and the effective availability of microbicidal Ag in thecomposition of Example 8 was much higher than that of Ag in NaAgZ usedas the comparison. Further, for the reasons already stated hereinbefore,microbicidal metal ions formed as a result of dissociation diffuse morerapidly in pores in the amtimicrobial composition of the presentinvention than in pores in the antimicrobial zeolite. Hence, thecomposition of the present invention should have a higher microbicidalefficiency than the antimicrobial zeolite and this is supported by thedata shown in table 12.

EXAMPLE 9

This example relates to the preparation of an antimicrobial compositionfor use in aqueous systems that contains silver as a microbicidal metal.

Three liters of desalted water was added to ca. 1.5 kg of crushed silicagel (product of Nishio Kogyo K.K.; specific surface area, 450 m² /g;pore size, 75 Å; pore volume, 0.8 cm 3/g; particle size, 30-60 mesh).The mixture was stirred at ca. 600 rpm to form a homogeneous slurry. Tothe slurry, a ca. 0.4N NaOH solution was added slowly until the pH ofthe slurry was finally adjusted to 9.5-10. Then, a solution having ca.65 g of NaAlO₂ dissolved in 3 l of water was added to the slurry and themixture was stirred at 25°±1° C. for ca. 11 hours at 600 rpm. Afterstirring, the mixture was filtered and the solid phase was washed withwater to remove excess alkali and unreacted NaAlO₂. During the washing,the pH of the filtrate was finally held at about 9. To the solid phase,a ca. 0.69M solution of silver nitrate was added and the resultingmixture was stirred continuously at 25°±1° C. over a period of ca. 8hours at 600 rpm. After the reaction, the mixture was filtered and thesolid phase was washed with water to remove excess silver ions. Thewashed product was dried at 100°-110° C. to obtain a dried antimicrobialcomposition for use in aqueous systems which contained silver as amicrobicidal metal according to the present invention.

This composition had a specific surface area and a pore volume of 328 m²/g (as measured by N₂ adsorption in the BET method) and 0.73 cm³ /g,respectively. The amount of silver as determined was 5.13% (on a drybasis). The composition contained 0.145 mmol of silver per 100 m² of thesurface area on a dry basis (see Table 13 below).

                  TABLE 13                                                        ______________________________________                                        Antimicrobial Composition for Use                                             in Aqueous Systems (Example 9)                                                Pore volume  Specific surface                                                                          Silver                                               (cm.sup.3 /g)                                                                              area (m.sup.2 /g)                                                                         (mmol/100 m.sup.2)                                   ______________________________________                                        0.73         328         0.145                                                ______________________________________                                    

In order to test the antimicrobial and/or microbicidal activity of theantimicrobial composition for use in aqueous systems which was preparedin Example 9, sewage was diluted with water to prepare two models ofwastewater as follows:

Model 1: COD=58 mg/l; E. coli count=3.1×10⁵ /ml

Model 2: COD=91 mg/l; E. coli count=4.6×10⁵ /ml (COD: Chemical oxygendemand)

Four grams of the dried product of the antimicrobial compositionprepared in Example 9 was added to 500 ml of wastewater Model 1. Thesame dried product was added in an amount of 6 g to 500 ml of Model 2.Both models were then stirred at 20°-25° C. for 10 hours at 500 rpm.Thereafter, the death rate of Escherichia coli in the wastewater wasmeasured in the usual manner.

The death rate of Escherichia coli was 100% in both wastewater Models 1and 2, demonstrating the high bactericidal activity of the antimicrobialcomposition for use in aqueous systems which was prepared in Example 9.

In order to check the water resistance of the antimicrobial compositionof the present invention for use in aqueous systems and its ability tomaintain the microbicidal activity, the following test was conductedusing the antimicrobial composition prepared in Example 9.

About twenty grams of the composition (dried product; particle size,30-60 mesh) was charged into a small glass ion-exchange column having aninside diameter of 22 mm. After backwashing with water, the compositionwas uniformly packed to form a bed. Tap water (Ca²⁺ =17 ppm; Mg²⁺ =6.9ppm; Cl=33 ppm; pH=6.7) was passed through the column at a flow rate of30±1.5 ml/min. When the amount of effluent emerging from the bottom ofthe column reached predetermined levels (see Table 14 below), a portionof the effluent was sampled and the concentration of silver in it wasmeasured by atomic-absorption spectroscopy. The results are shown intable 14.

                  TABLE 14                                                        ______________________________________                                        Water Passage Test                                                            Effluent (l)                                                                              Silver in effluent (ppb)                                          ______________________________________                                         10         5                                                                  30         6                                                                  70         5                                                                 100         4                                                                 200         7                                                                 300         6                                                                 500         6                                                                 ______________________________________                                    

As Table 14 shows, satisfactory results were obtained since the contentof silver in all samples of the effluent was very low within the rangeof 4-7 ppb. Throughout the passage of water, the composition experiencedno breakage, deformation, wear and other deterioration, indicating thegood water resistance of the composition.

After passing 500 l of water through the column, the spent antimicrobialcomposition was taken out of the column and the retention of itsantimicrobial and/or microbicidal activity was checked by the followingprocedure. a suspension (1 ml) containing no more than 10⁴ spores per mlof Aspergillus niger was injected and mixed with 9 ml of a suspension ofthe spent composition (300 mg/ml) and the mixture was held at 30° C. for24 hours. A portion (0.1 ml) of the mixture was dispersed in aSabouraud's agar medium and left to stand at 30° C. for 48 hours.Thereafter, the number of viable cells was counted to calculate thedeath rate of Aspergillus niger, which was 100%. The test resultsclearly show that the antimicrobial composition of the present inventionfor use in aqueous systems have strong antimicrobial and/or microbicidalactivity and exhibit the intended effect in water for a long time.

What is claimed is:
 1. An antimicrobial composition composed of a coatof aluminosilicate on the surface of silica gel, wherein saidcomposition has a pore volume of at least 0.3 cm³ /g and a specificsurface area of at least 100 m² /g, wherein said aluminosilicate coat iscomposed of either partial or complete substituted ion-exchangeablemetal (M) in the aluminosilicate solid coating layer represented by theformula

    xM.sub.2/n O.Al.sub.2 O.sub.3.ySiO.sub.2.ZH.sub.2 O,

wherein x and y represent the numbers of molecules of the metal oxideand silicon dioxide, respectively, M is an ion-exchangeable metal, n isthe atomic valence of M, and z is the number of molecules of water, andwherein said partial or completely substituted ion-exchangeable metal isselected from the group consisting of silver, copper, zinc, mercury,tin, lead, bismuth, cadmium, chromium and mixtures thereof.
 2. Anantimicrobial composition according to claim 1, wherein the metal ionshaving microbicidal action are present in a total amount of at least0.003 mmol per 100 m² of the surface coating of said composition.